1. Field of the Invention
The present invention relates to a resistance ladder network, more particularly to an R-2R type or 2.sup.n -R type resistance ladder network.
2. Description of the Prior Art
Resistance ladder networks are commonly used for digital-to-analog (D/A) converters. The resistors of a resistance ladder network are normally diffusion resistors and thin film resistors. The diffusion resistors are formed in a short strip form and so that all are fairly parallel. In the layout of the resistors, there must be a portion of wiring parallel to a diffusion layer forming the resistors, in other words a portion running from one end to the other of the diffusion layer. Therefore, it is not possible to form another wiring layer horizontally traversing the diffusion layer. If an insulation layer is inserted between the wiring, it is possible to form another wiring, but this has to be an unpreferable aluminum two-layer wiring and increases the number of masks in the manufacturing process. Thus, the yield rate decreases and the manufacturing process becomes more complex.